June 7, 2011 -- Testosterone decline is not inevitable with age, according to Australian scientists. Older men in excellent health can maintain their hormone levels, they say.

''What we found was, when you consider all the possible influences, age had no effect on testosterone levels in these very healthy men," says researcher David Handelsman, MD, PhD, director of the ANZAC Research Institute at the University of Sydney.

''By itself, age does not cause a lower testosterone in healthy men," he tells WebMD. "It's more likely that lowering of testosterone is a consequence of illnesses men acquire as they get older, like cardiovascular disease and obesity."

Handelsman presented his findings at The Endocrine Society's annual meeting in Boston.

However, a U.S.-based expert says the men in the study were ''super selected." They represent only a small portion of the aging male population.

The Healthy Man Study

Handelsman and his team looked at 325 men, all over age 40 and ranging from 40 to 97. They were enrolled in the Healthy Man Study in Australia.

All self-reported excellent health. They had no symptoms. The men's average body mass index (BMI) was 26; BMI below 25 is deemed healthy.

Those who took medications that affect testosterone were excluded.

The researchers took nine separate blood samples over a period of three months. They evaluated testosterone levels. Previous studies have looked at a single time point, Handelsman says.

"Their levels did not change over the three months," he says. More importantly, when the researchers looked at the entire sample of 325 men, even with the large age range, levels did not differ.

"Age alone does not make you testosterone deficient," Handelsman says.

If a man is found to have testosterone decline, he says, he and his doctor should look for underlying health problems that could be contributing.

The study was funded by the Medical Benefits Fund Foundation in Sydney. It is part of the private health insurer Bupa. Handelsman says Bupa had no input in the study.

Expert Disagrees

"He found men at one end of the spectrum," says Irwin Goldstein, MD, director of San Diego Sexual Medicine at Alvarado Hospital, San Diego. He reviewed the study findings for WebMD but was not involved in the study.

Over time, he says, testosterone levels in the general population tend to fall. The decline, he says, is about 1.5% per year on average. Over decades, it can add up to big decline.

Handelsman has a sample that does not represent the general population, he says. "In a population of people not super selected, we recognize there is an increasing prevalence of [lowered testosterone] with increasing age," says Goldstein, a clinical professor of surgery at the University of California San Diego.

Goldstein does agree with Handelsman that underlying health problems accounting for the lowered testosterone should be ruled out.

He reports consulting work for companies that make testosterone products, including Auxilium, Abbott, and Slate.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.